NAFO Sci Coun. Studies, 7: 53-59

Feeding of Roundnose Grenadier ( rupestris) and its Trophic Relationships in the North Atlantic*

A. V. Gushchin Atlantic Research Institute of Marine Fisheries and Oceanography (AtlantNIRO) 5 Dmitry Donskoy Street, Kaliningrad, USSR and S. G. Podrilzhanskaya All-Union Research Institute of Marine Fisheries and Oceanography (VNIRO) 17 V. Krasnoselskaya Street, Moscow, USSR

Abstract

The food spectra of roundnose grenadier from the continental slope areas of eastern Canada. West Greenland. Iceland and Hatton Bank and from the thalassobathyal zones of Reykjanes Ridge and the northern part of the Mid-Atlantic Ridge are compared and changes in feeding by region and fish size are demonstrated. Roundnose grenadier from the continental slope areas of the North Atlantic are shown to be consumers mainly of the second order. their food consisting typically of crustaceans (amphipods, euphausiids, mysids, small decapods and copepods). with fish and being generally of much less importance. In the thalassobathyal areas of the North Atlantic. roundnose grenadier are consumers of the third or fourth order. their food consisting mainly of various fish species (myctophids. bathylagids. serrivomerids. chauliodontids and searsiids) and large crustaceans (decap­ ods). The differences are discussed in relation to the environmental conditions and the trophic structures of the communities in the different regions.

Introduction eggs and larvae drift in the Irminger Current to West Greenland, from which the young are dispersed by the Roundnose grenadier are found on the slopes of Baffin Land and Labrador Currents to settle off Labra­ the continental shelves throughout the North Atlantic dor and northeastern Newfoundland, and that the mat­ from about 37° N off the United States coast northward uring fish return to the Icelandic area for spawning to Baffin Island, off West Greenland and Iceland, and in (Podrazhanskaya, 1971). The capture of roundnose the Barents Sea (Savvatimsky, MS 1969). They occur in grenadier in the pelagial over great depths (Haedrich, depths generally exceeding 400 m, and USSR investi­ 1974) is indirect evidence of migration opportunities gations in the Northwest Atlantic have shown that for the species. commercial concentrations exist off Newfoundland and Labrador in 500-1.000 m. Recent studies have Despite the opinions of some researchers that shown roundnose grenadier to be part of the ichthy­ are poor swimmers due to their body shape ofauna of Reykjanes Ridge and the northern part of the and are unlikely to undertake extensive migrations Mid-Atlantic Ridge (Gushchin and Kukuev, 1981), and (Savvatimsky, 1972; Parsons, 1976), some recent pap­ on the continental slope off Northwest Africa (Golo­ ers support, to a certain degree, the idea of population van, 1978). unity of roundnose grenadier throughout the North Atlantic (Alekseev et al., 1979; Marti, 1980; Zubchenko, Various aspects of the biology of roundnose gren­ 1981). In this paper, with the use of data on feeding of adier have been studied, e.g. age and growth by Savva­ roundnose grenadier in various regions, an attempt is timsky (1971,1972), parasites by Zubchenko (1981), made to show the position of the species in the trophic reproduction by Grigorev (1972) and Geistdoerfer system of the North Atlantic. (1979), and food and feeding by Podrazhanskaya (1971), Konstantinov and Podrazhanskaya (1972) and Gushchin (1982a). Conflicting hypotheses have Materials and Methods evolved from these and other studies on the extent of migrations and the population unity of roundnose The data in this paper were derived from analyses, grenadier in the North Atlantic. The absence of sexu­ by the authors and their colleagues, of the stomach ally mature individuals in Northwest Atlantic catches contents of roundnose grenadier which were collected from depths to 1,000 m and the discovery of spawning at different times by USSR research vessels in various grounds south of Iceland have led to the opinion that areas of the North Atlantic (Fig. 1). The laboratory

• Based on a paper presented at the NAFO Special Session on "Trophic Relationships in Marine Species Relevant to Fisheries Management in the NorthWest Atlantic", held at Leningrad. USSR. 14-16 September 1983. 54 Sci. Council Studies, No.7, 1984

A • Hatton North Reykjanes Ridge •

B

South Reykjanes• Ridge

c

Gibce• Fracture

o 3L • North Mid-Atlantic• Ridge

Fig. 1. The North Atlantic region showing the locations of round nose grenadier samples used in this paper. analyses involved 1,371 specimens from the Northwest by field analysis (incidence of food items) of large Atlantic in areas extending from West Greenland and numbers of stomachs from the Northwest Atlantic Baffin Island to the northern slope of Grand Bank off (>13,000) and from the Reykjanes Ridge and northern Newfoundland, 261 specimens from continental slope Mid-Atlantic Ridge in the Northeast Atlantic (>100,000 areas of the Northeast Atlantic (Iceland and Hatton specimens) (Podrazhanskaya, 1968, 1969, 1971; Kon­ Bank), and 1 ,330 specimens from Reykjanes Ridge and stantinov and Podrazhanskaya, 1972; Gushchin, northern Mid-Atlantic Ridge. 1982a). Also, the feeding relationships of deepwater ichthyofauna have involved the field (>8,600 speci­ The roundnose grenadier samples were examined mens) and laboratory (154 specimens) analyses of according to traditional methods of studying feeding stomachs of other fishes whict1 inhabit the same depth relationships in fishes (Borutskiy, 1974). At sea, the ranges and areas as roundnose grenadier in the North specimens without broken tails were measured as total Atlantic (Konstantinov and Podrazhanskaya, 1972; length in centimeters and weighed in grams, the Gushchin, 1982b). This paper incorporates informa­ degree of stomach fullness was estimated by the tradi­ tion from those studies in evaluating the feeding rela­ tional method used by Podrazhanskaya (1968, 1971), tionships between roundnose greandier and other and the stomachs were extracted and preserved in 4% species. formalin for laboratory analysis. The samples con­ tained specimens which ranged in length from 8 to 110 cm and had gonads at all maturity stages of the repro­ Results ductive cycle. In the laboratory, each stomach was weighed, and the food items were separated into iden­ Food composition by area tifiable components and weighed to the nearest 0.1 g. For analysis by area and fish size, the weights of the Northwest Atlantic slope areas. From the sampling various food components were expressed as percen­ of roundnose grenadier in various parts of the region, tages of the total weight of all food in the stomachs from Baffin Island and West Greenland southward to containing food. The total feeding index was calcu­ the Grand Bank, representatives of 74 different taxa lated as the ratio of total weight of food to total weight belonging to nine major groups of invertebrates and of fish sampled, multiplied by 10,000 (expressed as four families of fishes were found in the stomachs

0/000 ) . (Table 1). Empty stomachs generally constituted less than 30% of those examined from the various areas, In addition to the data summarized in this paper, except in Div. 3K and 3L where 66 and 81 % respectively the feeding of roundnose grenadier has been studied were empty, the latter value being based on a very GUSHCHIN and PODRAZHANSKAYA: Feeding of Roundnose Grenadier 55

TABLE 1. Food composition of roundnose grenadier (% by weight) from various areas of the North Atlantic. (See Fig. 1 for locations of areas sampled.)

Northwest Atlantic areas Northwest Atiantic slope areas Slope areas Thalassobathyala. Stomach contents o 2G 2H 2J 3K 3L Iceland Hatton A B C D Cephalopoda 5.4 8.7 9.4 2.9 8.2 3.3 1.1 2.6 9.0 7.0 24.6 4.3 5.5 Chaetognatha 0.6 1.8 1.3 5.8 2.4 0.2 0.3 0.2 0.0 0.1 0.0 Polychaeta 2.5 0.3 0.8 0.1 1.5 0.0 0.0 0.0 0.0 Scyphozoca 8.9 4.0 1.7 3.5

Tunicata 1.9 1.2 0.9 1.3 3.1 0.8 0.3 0.3 0.1 0.1 Crustacea 85.0 70.9 53.0 84.3 57.8 91.5 27.3 88.1 76.3 14.5 18.7 36.2 23.7 49.0 28.2 35.9 76.6 25.4 3.8 0.4 1.0 0.8 0.6 1.3 0.1 Copepoda 5.1 1.6 8.5 0.8 6.6 1.5 4.6 0.1 0.5 0.1 0.2 1.3 0.3 Decapoda 4.4 12.9 2.1 2.3 13.2 84.5 18.5 51.4 55.9 7.8 12.7 19.8 18.9 Eu phausiacea 5.4 9.8 6.5 4.6 12.6 1.7 35.5 0.4 1.2 0.4 0.4 Isopoda 0.1 0.0 0.4 0.1 Mysidacea 21.1 18.4 0.0 3.8 0.1 11.9 3.1 3.1 8.4 3.2 Ostracoda 0.4 0.3 0.3 0.0 Unidentified 7.5 2.3 0.6 4.3 0.7 Pisces 6.5 8.3 30.5 2.7 28.8 0.8 70.2 4.8 12.2 67.5 52.1 57.0 66.0 Bathylagidae 28.4 7.9 1.7 8.8 Chauliodontidae 3.4 2.5 5.4 4.0 Cottidae 2.8 Malacosteidae 5.8 5.8 Melamphaidae 2.0 1.9 3.5 0.9 Myctophidae 2.1 22.6 0.3 1.6 69.6 12.2 10.4 8.8 10.6 28.6 Paralepididae 10.9 Scorpaeidae 0.6 7.2 Searsiidae 4.3 1.5 11.8 Serrivomeridae 7.9 19.0 18.3 1.8 Unidentified 3.8 5.5 7.9 2.4 18.0 0.8 0.6 4.8 6.5 7.7 10.2 4.3 Unidentified food 8.1 3.8 3.3 1.1 1.4 3.4 2.5 1.6 0.3 0.6 1.2 Total stomachs 727 156 97 79 125 172 15 236 25 578 255 338 159 Empty stomachs (%) 29.2 25.6 24.7 18.9 8.8 66.3 81.0 6.8 40.0 44.2 14.2 27.2 17.0 Feeding index (0/000) 64 28 20 34 35 7 20 43 36 35 39 27 32 a A = North Reykjanes Ridge, B = South Reykjanes Ridge, C = Gibce Fracture, D = North Mid-Atlantic Ridge. small sample. The feeding index was highest in Sub­ with crustaceans and fish being the major compo­ area 0 and lowest in Div. 3K. Invertebrates predomi­ nents. Among the crustaceans. amphipods were domi­ nated with considerably more than 50% of the food (by nant in both divisions but decapods and euphausiids weight) consisting of crustaceans. mainly amphipods were also significant in Div. 2J. In contrast. the round­ (Parathemisto /ibellu/a. P. abyssorum). copepods nose grenadier off central Labrador (Div. 2H) fed (Ca/anus hyperboreus. C. finmarchicus). euphausiids mainly on crustaceans (amphipods). with fish and (Meganyctiphanes norvegica. Nematoscelis meg­ other invertebrates being rather insignificant. Off a/ops). and decapods (). Other invertebrates northeastern Newfoundland (Div. 3K). the diet again consumed in small quantities in most areas were consisted mainly of crustaceans but decapods cephalopods. chaetognaths. polychaetes and tuni­ replaced amphipods as the major food type. On the cates. Fish were eaten in variable amounts in all areas. northeastern slope of Grand Bank (Div. 3L). fish (myc­ with myctophids being the most consistent group. tophids) was the main component in the very small number of specimens examined. The composition of food organisms in the stom­ achs varied somewhat in different areas of the North­ Northeast Atlantic slope areas. Like most of the west Atlantic (Table 1). In the northern areas (Sub­ Northwest Atlantic samples. crustaceans comprised areas 0 and 1). the food consisted. mainly of the major food component in the specimens from Ice­ crustaceans. with amphipods (hyperiids) and mysids land and Hatton Bank (Table 1). with other inverte­ being the main components in both areas and decap­ brates and fish being relatively unimportant. ods () and euphausiids being also significant in Crustaceans were represented by decapods and Subarea 1. Off northern and southern Labrador (Div. euphausiids in the Iceland sample and mainly by 2G and 2J). the stomach contents were quite similar. decapods with some mysids in the small sample from 56 Sci. Council Studies, No.7, 1984

Hatton Bank. Although the feeding index was similar in TABLE 2. Food composition (% by weight) of roundnose grenadier both cases, only 7% of the Iceland specimens had from the continental slope areas of the Northwest Atlantic empty stomachs. and Iceland by size groups.

Percent food by fish size (cm) Northeast Atlantic thalassobathyal. The food com­ positon of roundnose grenadier in the thalassobathyal Stomach contents ~40 41-100 >100 of Reykjanes Ridge and the Mid-Atlantic Ridge Cephalopoda 6.6 9.2 included more than 90 different types of organisms Chaetognatha 0.4 1.2 which constitute the macroplankton and micronekton Polychaeta 2.0 communities over the summits of the underwater mounts. In the four areas where samples were col­ Tunicata 0.7 2.3 lected, representatives of 11 major groups of inverte­ Crustacea 90.1 82.0 55.3 brates and eight families of fish were found in the Amphipoda 66.3 22.8 2.6 Copepoda 10.2 5.1 stomachs (Table 1). There were practically no bottom 0.9 Oecapoda 16.4 35.3 or near-bottom organisms. Empty stomachs consti­ Euphausiacea 4.7 14.9 16.1 tuted 14-44% of those examined from the different Mysidacea 8.9 22.8 0.4 areas, and the feeding index varied over a relatively Pisces 7.5 33.2 narrow range (27-390/000). Fishes were represented Unidentified food 9.5 0.0 mainly by Myctophidae (Benthosema glaciate, Lampa­ nyctus crocoditus) , Serrivomeridae (Serr;vomer bean i) Total stomachs 111 1,449 47 and Bathylagidae (Bathytagus euryops); crustaceans Empty stomachs (%) 5.4 33.6 8.5 were represented mainly by shrimps (Acanthephyra, Feeding index (0/000) 67 45 37 Pasiphae, Gennades, Sergestes); and cephalopods were represented by squids (Mastegoteuthis agassiz;, the food of small grenadier «40 cm) consisted of crus­ Gonatus fabricii, Todarodes sagittatus). taceans, with amphipods (hyperiids) being the major component followed by copepods and mysids. Gren­ Unlike round nose grenadier from the Northwest adier of intermediate sizes (41-100 cm) also fed mainly and Northeast Atlantic continental slopes, those from on crustaceans, with hyperiids and mysids being the the thalassobathyal fed mainly on various fishes, with major components although decapods and euphau­ crustaceans being second in importance (Table 1). siids were also important. Fish and cephalopods were Among the fish types consumed in the northern part of present in small quantities. The largest grenadier Reykjanes Ridge (area A), bathylagids were dominant (>100 cm) fed mainly on crustaceans (decapods) and with paralepidids, myctophids, serrivomerids and fish (mostly myctophids). chauliodontids being of lesser importance. In the southern part of the Ridge (area B), serrivomerids were Northeast Atlantic thalassobathyal. In these areas dominant, with myctophids and bathylagids being next (Table 3), young roundnose grenadier (8-20 cm) fed in importance. In the Gibce Fracture sample (area C), mainly on mysids, with chaetognaths and copepods fish food consisted mainly of serrivomerids and mycto­ being of much less importance. This may not be repre­ ph ids, whereas, farther southward on the northern part sentative because the sample consisted of only 8 spec­ of the Mid-Atlantic Ridge (area 0), myctophids fol­ imens. In larger juveniles (21-40 cm), although the lowed by searsiids and bathylagids were the dominant proportion of mesoplankton crustaceans decreased types. Among the crustaceans, decapods (shrimps) significantly, mysids and copepods continued to be were important in all four areas and mysids were found the major food components. Additionally, small consistently in smaller quantities. Among the other mesopelagic fishes became important as food, the invertebrates, cephalopods and scyphozocans were major types being melamphaids and myctophids. The rather important in the Reykjanes Ridge samples. proportion of crustaceans increased slightly for larger fish (41-60 cm) due to the appearance of decapods Food composition by size-group (shrimps) in the diet. The overall proportion of fish Northwest Atlantic and Iceland slope areas. The food remained about the same forthis size group as for composition and quantity of food in the stomachs of the 21-40 cm group but more families were repres­ round nose grenadier varied considerably from the ented, the most significant ones being Melamphaidae, smallest to the largest specimens, but there was little Serrivomeridae and Bathylagidae. Grenadiers larger variation among fish of intermediate sizes and data for than 60 cm fed mainly on a variety of fishes (Myctophi­ 41-100 cm specimens were combined (Table 2). Also, dae, Serrivomeridae, Bathylagidae and Chauliodonti­ the data for Iceland were included with those from the dae), but crustaceans (shrimps). cephalopods and Northwest Atlantic because of the similarity of the food scyphozocans were consistently found in smaller fauna in the samples from the two regions. Nearly all of quantities. GUSHCHIN and PODRAZHANSKAYA: Feeding of Roundnose Grenadier 57

TABLE 3. Food composition (% by weight) of roundnose grenadier from the thalassobathyal areas of the Northeast Atlantic by size groups.

Percent food by fish size (cm)

Stomach contents 8~20 21-40 41-60 61-80 81-100 Cephaiopoda 4.9 12.8 6.0 Chaelognatha 14.9 7.1 0.7 0.1 0.0 Scyphozoca 3.3 7.3 Tunicala 0.5 0.3 0.0

Crustacea 85.0 51.8 53.9 14.2 15.0 Amphipoda 2.5 0.6 0.7 Copepoda 4.2 10.3 3.2 0.4 0.1 Decapoda 3.8 22.3 8.4 10.1 Euphausiacea 0.7 0.7 0.3 Isopoda 2.1 0.0 0.0 Mysidacea 77.0 36.0 12.7 2.9 3.3 Ostracoda 1.2 0.2 0.0 Unidentified 3.8 1.7 9.2 1.0 0.5

Pisces 0.1 41.1 39.8 69.3 71.7 Bathylagidae 6.2 11.8 12.1 Chauliodontidae 2.0 9.9 Malacosteidae 5.8 Melamphaidae 18.S 14.2 3.5 0.6 Myctophidae 10.1 1.1 12.3 26.5 Searsiidae 0.1 5."7 0.7 Serrivomeridae 13.9 13.9 14.1 Sternoptychidae 9.8 0.3· 0.3 Unidentified 0.1 2.4 4.2 14.0 7.5 Total stomachs B 52 66 393 282

Empty stomachs (%) 25.0 17.3 4.6 9.4 13.1

Feeding index (%00) 81 75 28 38 36

Discussion and Conclusions TABLE 4. Variation in mean index of degree of stomach fullness of roundnose grenadier by month in the thalassobathyal of the North Atlantic. based on field examination of speci- The seasonal dynamics of roundnose grenadier mens. feeding in the North Atlantic, as reported by Podraz­ No. of Mean Standard hanskaya (1968, 1969, 1971) is manifested by an Month specimens index deviation increase in the numbers of stomachs containing food Mar 2.900 1.27 0.16 from spring to autumn, with major feeding in Septem­ Apr 12,500 1.14 0.10 ber-November during the biological autumn (Semen­ May 14,900 0.84 O.OS ova, 1964). Hepatosomatic indices closely coincide Jun 19,600 0.75 0.07 with the increase in feeding activity from spring to Jul 20,100 0.74 0.07 autumn (Podrazhanskaya, 1969). The feeding of Aug 9,900 0.86 0.09 Sep 10.500 0.95 0.11 roundnose grenadier on macroplankton, bathypelagic Oct 7,200 1.12 0.11 crustaceans and some fish in the Northwest Atlantic Nov 2,600 0.S3 0.23 indicates that roundnose grenadier is a consumer of Dec 2,400 0.54 0.14 the second or third order (Fig. 2), i.e. it utilizes the energy from phytoplankton through one or two levels (Table 4). Roundnose grenadier in this region are con­ of prey organisms. The energy link to bottom orga­ sumers of the third or fourth order (Fig. 3), i.e. their nisms is mainly through shrimp (Panda/us borealis) energy is derived mainly from eating fish in the which feed on polychaetes. bathypelagic zone and to a lesser degree from eating crustaceans and organisms of a stationary trophic The seasonal dynamics of roundnose grenadier in complex. Meanwhile, roundnose grenadier are con­ the thalassobathyal is manifested by decreasing sumed by predators of higher trophic levels: dogfishes amounts of food in the stomachs from March to (Etmopterus spinax, Centroscyllium fabricii), north.! July-August, increasing amounts during spawning in ern wolffish (Anarhichas denticulatus), cutlassfish September-October after which the autumn maximum (Aphanopus carbo), deepsea angler (Ceratias ho/­ is rec.orded, and decreasing amounts during the winter boelli), and toothed whales. 58 Sci. Council Studies, No.7, 1984

Reinhardtius hippogJossoides Etmopterus spina x I Centroscyllium fabricii ~ Anarhichas denticu/atus Aphanopus carbo r-f }- Ceratias ho/boelli t Amphipoda, Euphausiacea + Cephalopoda, Chaetognatha Coryphaenoides rupestris I Pisces + Chauliodontidae, Malacosteidae 7 Myctophidae, Serrivomeridae Copepoda Cephalopoda 4- Mysidacea Decapoda ~ Tunicata + Bathylagidae, Searsiidae t + Decapoda, Mysidacea I Phytoplankton Detritus I Fig. 2. Trophic relations of roundnose grenadier on the continental r Cyclothone, Ostracoda slopes of the Northwest Atlantic. Euphausiacea, Copepoda I If roundnose grenadier on the continental slopes + of the Northwest Atlantic and in the thalassobathyal of I Phytoplankton I Reykjanes Ridge and northern Mid-Atlantic Ridge belong to the same population, as has been hypothes­ Fig. 3. Trophic relations of roundnose grenadier in the thalasso­ bathyal areas of Reykjanes Ridge and northern Mid-Atlantic ized by various researchers (Podrazhanskaya, 1971; Ridge. Alekseev etaI. 1979; Marti, 1980, Zubchenko, 1981), the area of distribution may be considered to consist of found in transformed water masses which are formed two functional parts (feeding and spawning migra­ by the interaction of North Atlantic and Subarctic tions). From the spawning area of Reykjanes Ridge and water masses (Mamaev, 1960; Stepanov, 1974), with a northern Mid-Atlantic Ridge, developing eggs and lar­ number of "zones of microproductivity" in the pelagial vae are transported by currents to the Northwest Atlan~ over the summits of the undersea mounts (Bezrukov tic via South Greenland, and the young settle on the and Natarov, 1976; Shomura and Barkley, 1979). These continental slopes off Baffin Island, Labrador and east­ "zones", in combination with a number of frontal ern Newfoundland (Marti, 1980; Zubchenko, 1981). As zones, according to Andriyashev (1979), create the they grow in size, the fish move northward along the high productivity of these thalassobathyal areas. slope towards Greenland and then eastward to Iceland Therefore, the fauna in these areas contain an abun­ where the larger maturing individuals aggregate and dance of tropical and subtropical oceanic species perform a spawning migration southward along Reyk­ (Gush chin and Kukuev, 1981) with a complex structure janes Ridge. of trophic chains. Roundnose g renadierfeed mainly on fishes in this region, thus being consumers of the third Roundnose grenadier of the North Atlantic inhabit or fourth trophic levels. It is noteworthy that round nose waters of the intermediate structural zone. In the grenadier in this region tend to be larger than those on Northwest Atlantic, this zone, according to Stepanov the continental slopes of the Northwest Atlantic. Thus, (1974), is represented by subarctic water which con­ roundnose grenadier rationally utilize the available tains the arctoboreal fauna with an abundance of crus­ food resources in both extremes of the distribution taceans (Beklemishev, 1969). This mayaccountforthe area in the North Atlantic. predominance of crustaceans in the food of roundnose grenadier in most areas of the Northwest Atlantic. However, on the northeastern slope of Grand Bank where the subarctic and transformed waters border References upon the southern boundary of arctoboreal fauna, roundnose grenadier were found to feed mainly on fish ALEKSEEV, F. E., E. I. ALEKSEEVA, and N. V. TITOVA. 1979. Polymor­ (Table 1). phic muscle esterases, ecological structure of settlements and studying of the structure of grenadier populations ( rupestris Gunn.). In Biochemical and population genetics of In the spawning area of Reykjanes Ridge and fishes, V. S. Kizpichnikov (ed.), Tr. Ins!. Tsitologii Akad. Nauk northern Mid-Atlantic Ridge, round nose grenadier are SSSR, Leningrad, p. 58-63. GUSHCHIN and PODRAZHANSKAYA: Feeding of Roundnose Grenadier 59

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